The introduction of synthetic organic pesticides following World War II brought inestimable benefits to humanity and agricultural economic profitability. Application of broad-spectrum pesticides is the primary method used for controlling fungal and insect pests. For example, the widescale deployment of DDT resulted in the complete riddance, from entire countries, of serious public pests such as malaria mosquitoes. However, there were warnings about the hazard of unilateral approaches to pest control.
The development of new pesticides and the increasing amounts of pesticides used for pest control are closely correlated with the development of pest resistance to chemicals. The number of pesticide resistant species has greatly increased since the adoption of DDT in 1948. As a result, by the 1980s, the number of reports of pesticide resistance for arthropod pests was listed as 281, for plant pathogens 67, and for weeds 17. These numbers have steadily increased to the present day. Thus, the need for biological control agents, especially those with broadbase activity is especially important.
One approach that is gaining significant attention is the use of agricultural cultivars that are resistant to pests. These cultivars can be developed by the transgenic introduction of target specific natural resistance factors. However, to enhance host-plant resistance, it is necessary first to identify and to characterize target-specific factors that will significantly reduce the population(s) of herbivorous insect(s).
Only a limited number of natural products have been characterized and identified as effective defensive agents against herbivorous insects, few of these are proteins (e.g., proteinase inhibitors, arcelin, alpha-amylase inhibitors, lectins, endotoxin from Bacillus thuringiensis, and lipoxygenases), and even fewer are target specific (Duffey, et al., "Plant Enzymes in Resistance to Insects," In J. R. Whitaker and P. E. Sonnet (eds.), Biocatalysis in Agricultural Biotechnology, American Chemical Society, Washington, D.C. (1989); Gill, et al., "The Mode of Action of Bacillus thuringiensis Endotoxins," Ann. Rev. Entomol., 37:615-36 (1992); Hedin, P. A., "Plant Resistance to Insects," American Chemical Society, Washington, D.C., p. 375 (1983); Rosenthal, et al., "Herbivores--Their Interaction with Secondary Plant Metabolites," Academic Press, New York, p. 718 (1979). Identification and characterization of proteins as resistance factor(s) enables the isolation of gene(s) that encode(s) these proteins. These genes can be transgenically inserted into agricultural crops, which may enhance the resistance of these crops against herbivorous insects without altering desirable characteristics of the cultivar(s) (Fraley, et al., "Genetic Improvements of Agriculturally Important Crops," Cold Spring Harbor Laboratory, p. 120 (1988); Hilder, et al., "A Novel Mechanism of Insect Resistance Engineered into Tobacco," Nature, 330:160-63 (1987); Ryan, C. A., "Proteinase Inhibitor Gene Families: Strategies for Transformation to Improve Plant Defenses Against Herbivores," BioEssays, 10:20-24 (1989); Vaeck, et al., "Transgenic Plants Protected from Insect Attack," Nature, 328:33-27 (1987).
One target that has been selected is a structural polymer, chitin, which is present in insects and some fungi that attack plants, but is absent in higher plants and vertebrates. U.S. Pat. No. 4,751,081 follows this approach and is directed to novel chitinase producing bacteria strains for use in inhibiting chitinase sensitive plant pathogens (i.e. fungi and nematodes). However, the approach of U.S. Pat. No. 4,751,081 lacks flexibility.
The present invention is directed to controlling fungi and insects that attack plants.